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Serology

Serology. The study of body fluids. Serology-Definition. The study of antigen/antibody reaction The study of biological fluids Blood, sweat, tears, saliva, semen, etc. But, I was not even at the crime scene…. If you leave behind a body fluid sample, it proves your presence at the scene.

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Serology

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  1. Serology The study of body fluids

  2. Serology-Definition • The study of antigen/antibody reaction • The study of biological fluids • Blood, sweat, tears, saliva, semen, etc.

  3. But, I was not even at the crime scene… • If you leave behind a body fluid sample, it proves your presence at the scene. • Serological evidence has more weight than fingerprinting. • Often used in cases of paternity and ancestry

  4. Quiz… • What is the most common body fluid left behind at a crime scene? • Blood

  5. Blood Info • Plasma • Liquid portion of whole blood • Contains proteins, enzymes, clotting factors, electrolytes, and 3 types of cells • Leukocytes – white blood cells • Erythrocytes – red blood cells • Platelets – cells involved in clotting

  6. Blood Serum • When blood clots and the clotted material is removed, a yellowish liquid remains • Yellowish fluid is serum • Serum contains the majority of proteins and enzymes • Serum contains the antibodies

  7. Important components • 2 components of blood are very important to forensic scientists • RBC’s and serum • With these two components, a serologist can determine blood type from any sample or stain • With more than 100 blood factors known, it is theoretically impossible for two people other than identical twins to have the same combination of blood factors.

  8. Blood Types • Dr. Karl Landsteiner – responsible for ABO blood typing system, allowed for safe matching of blood donor to recipient • Knowing the blood type helps to narrow the suspect list

  9. Blood Types • Determined by antigens present on cells • A – a antigen • B – b antigen • D antigen – Rh factor • Found in most people, responsible for violent antigenic reactions • Can be harmful if Rh negative meets Rh positive during mating

  10. Antigens • A substance, usually a protein, that stimulates the body to produce antibodies to fight an intrusion • There are more than 15 known blood antigens

  11. Antibody • For every antigen, there is an antibody • An antibody is highly specific, this means that only recognizes and interacts with its specific antigen • The combination of antigen and antibody forms an antigen-antibody complex – the basis for blood typing

  12. How do you type blood? • Use antiserum to test for agglutination (clumping) • Anti A – will make type A clump • Anti B – will make type B clump • Type O will not clump with either Anti A or Anti B • Anti Rh – will make Rh+ clump

  13. Some Blood Statistics • 43% of Americans have type O • 42% of Americans have type A • 12% of Americans have type B • 3% of Americans have type AB

  14. Who is the Universal Donor? • A- receive blood from A & O • Give to A & AB • B- receive blood from B & O • Give to B & AB • AB- receive blood from A, B, AB, O • Give to AB • AB is the Universal Receiver • O- receive blood from O • Gives to A, B, AB, and O • O is the Universal Donor

  15. What to do with crime scene blood… • Type each blood sample separately • At scenes with multiple victims, typing and antigen-antibody complexes help reconstruct crime scene

  16. How much blood is needed? • Modern technology allows us to test minute amounts of blood, but the sample does not hold substantial weight like a large sample • Chemical reactions from the antigens and DNA fingerprinting could degrade small samples • Putrefaction- the decay of cells due to bacterial activity in old samples

  17. What is done with blood evidence? • Typing often tells the story of how and when things happened • Time of bloodstain is difficult to determine • Exclude suspects • Extract DNA

  18. Secretors • A secretor is a person who provide blood typing requirements in all body fluids. • Examples: saliva, semen, gastric juices, etc. • Do not confuse blood typing with DNA typing – you can obtain DNA from all body fluids of every person • DNA TYPING AND BLOOD TYPING ARE NOT THE SAME THING

  19. How do you know if a stain is blood? • Presumptive Testing • Kastle-Meyer Color Test • Hemastix • Luminol • Specific Testing • Microcrystalline Test • Precipitin Test

  20. Kastle-Meyer Color Test • Blood stain + phenolphthalein + hydrogen peroxide = deep pink color • Being a color test, it is only considered presumptive • False Positives: Potatoes and Horseradish

  21. Hemastix Test • Hemastix strip moistened with distilled water + blood sample = green color • Also a color test and thus is presumptive

  22. Luminol Test • Luminol + blood + dark = light • Must be viewed in the dark • Extremely sensitive • Can detect bloodstains diluted up to 10,000,000 times • Does not interfere with DNA testing

  23. Microcrystalline Test • Confirmative test • 2 popular versions • Takayama • Teichmann • Both versions depend on chemical additions to the blood • Test is susceptible to interferences of contamination

  24. Precipitin Test • Human antiserum added to blood sample • If agglutination occurs, then the sample is human blood • 2 methods: capillary tube, gel diffusion • Can be used on samples up to 10-15 yrs old • Has produced positive test on 4-5 thousand year old mummies

  25. Not human blood? • You can still use the precipitin test with other antiserums • Using a species specific antiserum, a serologist can determine the source of the blood

  26. DNA Fingerprinting/Typing • Testing for paternity • You inherit your blood type from your parents • Paternity confirmation plays a role in child support, custody, visitation • Also has role in crimes that involve kidnapping, insurance fraud, and inheritance

  27. Heredity • Transmission of hereditary material is done through genes • Genes are found on chromosomes • Humans have 46, 23 from mother, 23 from father, found in pairs resulting in 23 chromosomes in normal cells • XX – female • XY – male • Females always donate X, Males donate either X or Y

  28. Genetics • Locus- Position of a gene on a chromosome • Alleles- alternative forms of genes • Homozygous- AA, aa • Heterozygous- Aa • Dominant- always represented • Recessive- not seen if dominant is present • Codominant- not seen in full effect

  29. Genetics continued… • Genotype- specific genetic make-up • Phenotype- observed characteristics • Punnet Square- diagram of genetic possibilities

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